Phase-sensing electro-optic field sensors that are already in use are of two basic types, polarimetric and interferometric. The polarimetric types include those based on the Pockels, Kerr, and Faraday effects. The interferometric typic are usually based on Mach Zehnder, Michelson, and Fabry Perot interferometers, ring resonators, and mode couplers. The two-beam interferometric types, i.e., the Mahc Zehnder and Michelson interferometers, may use equal or unequal optical paths in the two branches of the interferometer. Usually, one branch of the interferometer will contain an electro-optic crystal whose index of refraction is dependent on the eletric field in which it is placed.
As all of these types of interferometers are commonly constructed, several optical elements, such as beam splitters and mirrors are used to separate and recombine the beams. These elements are extremely sensitive to alignment, vibration, and thermal distortion. In order to avoid these effects, the branches of the interferometers may be made as channels in a dielectric plate of low coefficient of expansion, such as quartz or low-expansion ceramic glass. This is a very delicate, and usually an extremely expensive procedure.